The present invention relates to a lighting system, for example a lighting system for domestic or work premises, but also for public places, hotel or industrial buildings, urban centers, streets, and generally for environments in which it is useful or necessary to provide lamps or lighting fittings which have a light intensity regulation function, or which in other words are “dimmable”.
Lamps known as “dimmable”, in other words those provided with regulators of their light emission, are used increasingly often for lighting many environments, particularly domestic and work environments.
Lamps fitted with these devices can be regulated in such a way as to vary the light intensity according to the requirements of the user and/or the ambient light, for example the light from a window. Typically, dimmable ballasts, in other words ballasts containing brightness regulation circuits, are provided for regulating the light emission of HID lamps or other lamps supplied through ballasts. These ballasts require a brightness regulation signal, typically a low-voltage signal at 0–10 V, at their inputs, in addition to the electrical power network voltage. They have low-voltage control terminals, across which a potentiometer or other device for regulating the dimming signal is connected.
Devices for regulating the emission of lamps are known and are produced by many companies in this field. An example of a device of this type is the regulator produced and distributed by Osram, Germany, under the brand name Quicktronic®.
A very simple installation circuit for these devices is shown in FIG. 1. The number 1 indicates a dimmable ballast for supplying a lamp 2. The ballast is connected to the electrical power supply line 3, shown schematically as a live line L, a neutral line N and a ground line G. The number 5 indicates a potentiometer which serves to control the low-voltage signal for regulating the light emission of the lamp 2. A switch 7 is also provided for switching the lamp on and off. The switch 7 and the potentiometer 5 must be located in a position that is easily accessible to the user, and can, for example, be placed together in a single box.
Clearly, when a conventional lamp is to be replaced with a lighting fitting provided with a brightness regulator, an engineering operation is required. This is because the dimmable ballast 1 and the lamp form a single assembly which can be simply substituted for the conventional fixed emission lamp, and therefore the connections to the live line L, the neutral N and the ground G of the line 3 can be made easily without any special operation, leaving the switch 7 in the same position as the switch of the original lamp. On the other hand, the installation of the potentiometer 5 requires the installation of a dedicated electrical line 9 for the dimming signal.
Then this operation has to be carried out in an apartment or in a workplace, it will cause considerable problems and inconveniences, in addition to the costs due to this operation. Even when the use of a dimmable lamp is specified in a newly produced installation, the necessity of providing two connection lines (to the electrical power supply and to the potentiometer) complicates the installation.
If the installation comprises a plurality of lamps with regulation of the light emission, it is necessary to provide a plurality of potentiometers and consequently a plurality of lines 9, unless only a single potentiometer is used, in which case it will not be possible to regulate the light emission of the various lamps independently of each other. This evidently limits the flexibility of use.
Moreover, while it is easy to provide a plurality of on-off switches 7 at different points of a single environment or apartment, it is difficult to be able to regulate the light emission from a plurality of dispersed points.
In the lighting of public places, urban centers, highways and the like, there arises a similar problem of reducing the light flux of lamps in the middle of the night, in order to save energy. At present, this is done by reducing the supply voltage in the electrical supply network of the various lighting fittings. Essentially, the electrical power supply line of one or more lighting units includes a flux regulator, which receives at its input electrical energy at the normal power network voltage, typically 230 V, and has its output connected to the power supply line of the lighting units. The output voltage is controllable. When full illumination is required, the output voltage from the regulator is 230 V, while it is reduced in the middle of the night, typically to 180 V, thus reducing the light emission of the lamps supplied through the regulator.
This system has considerable drawbacks. This is because the power supply line of the lighting units is frequently very extended and therefore considerable losses of load occur in the line, especially when the voltage is reduced. The discharge lamps used for this type of application cannot remain illuminated if the supply voltage falls below a certain minimum value. In many situations, therefore, the lighting units farthest from the flux regulator, whose terminals receive a voltage which is lower than that at the output of the flux regulator, due to losses in the supply line, cannot remain illuminated.